Effects of untreated and heat-treated canola presscake on milk yield and composition of dairy cows

Five primiparous and five multiparous Holstein cows were used in two Latin square design experiments to determine effects of feeding unheated and heat ed canola presscake on milk yield and composition, and milk fatty acid conc entrations of lactating dairy cows. Five diets that differed in level and s ource of dietary fat were formulated: a low fat control diet with 30 g kg(- 1) fat from tallow, an unheated canola presscake supplemented diet (50 g kg (-1) fat), a heated canola presscake supplemented diet (50 g kg(-1) fat), a high tallow plus unheated canola meal supplemented diet (50 g kg(-1) fat), and a high tallow plus heated canola meal supplemented diet (50 g kg(-1) f at). In sacco ruminal degradability of heated and unheated canola presscake was compared with that of heated and unheated canola meal in a randomized complete block design using two ruminally fistulated cows. Heat treatment r educed ruminal DM and CP degradability of canola presscake. Multiparous cow s fed diets supplemented with heated or unheated canola presscake produced more milk than those fed diets containing similar levels of fat from tallow with heated or unheated canola meal, respectively. High levels of fat from any diet reduced milk fat percentage for cows of either parity. Feeding he ated canola products increased milk and milk protein yields in primiparous cows only, but cows of both parities fed diets containing canola presscake produced milk with lower concentrations of C12:0, C14:0, and C16:0 fatty ac ids than cows fed the canola meal and tallow diets, although concentrations of C18:1 n-9 were unaffected by fat source or level. Feeding canola produc ts to dairy cows can alter milk fatty acid profile, but only primiparous co ws have increased productivity as a result of feeding heated, versus unheat ed, canola presscake. (C) 2001 Elsevier Science B.V. All rights reserved.